German Patent Application No. 43 05 155 (corresponding to U.S. Pat. No. 5,455,770) describes a driving dynamics control system having a higher-ranking driving dynamics computer. A braking controller and a rear axle steering controller are subordinate to the vehicle dynamics computer. The subordinate braking controller has a yaw velocity controller and a float angle controller. The subordinate rear axle steering controller has a yaw velocity controller and a float angle limiter. The two controllers, the braking controller and the rear axle steering controller, may operate at the same time.
With the help of measured data acquisition, various quantities are detected, such as the yaw velocity, the float angle, the wheel velocities, the steering angle for the front and rear axles, the longitudinal and transverse velocities of the vehicle and the longitudinal and transverse accelerations of the vehicle. Data obtained by measured data acquisition is available to the vehicle dynamics computer, the subordinate braking controller and the subordinate rear axle steering controller. On the basis of the driving situation, which is described by the data compiled with the help of measured data acquisition, the vehicle dynamics computer defines a setpoint for the yaw velocity and a limit value for the float angle for the vehicle dynamics computer. At the same time, the vehicle dynamics computer notifies the braking controller of the control mode, i.e., whether a yaw velocity control or a float angle control is to be carried out. On the basis of these setpoints, the braking controller initiates control actions for a wheel controller subordinate to it, the wheel controller determining as a function of these actuating signals valve opening times which are converted to wheel brake pressure changes by a suitable hydraulic system. Depending on the setpoints for the braking controller, the vehicle dynamics computer also defines a setpoint for the yaw velocity and a limit value for the float angle for the rear axle steering controller. Furthermore, the vehicle dynamics computer informs the rear axle steering controller which of the two controllers implemented in it is to be operative. The two controllers included in the rear axle steering controller generate signals that characterize the rear axle steering angle and are converted by an appropriate hydraulic system.
German Patent Application No. 40 31 316 (corresponding to U.S. Pat. No. 5,205,371) describes a steering system and will be explained in greater detail below due to its relevance for an understanding of the present invention. With such a steering system, the steering movements imposed by the driver using the steering wheel, steering wheel angle .delta..sub.L detected by a sensor, are superimposed on the movement of an actuator, namely motor angle .delta..sub.M in a superpositioning gear. Resulting superimposed movement .delta..sub.L ' is relayed via the steering gear and steering linkage to the front wheels, which are designed to be steerable, to set steering angle .delta..sub.V. The actuator may be designed as an electric motor. The operating principle of such a power-assisted steering system is based on the fact that steering can be made very indirect by translation i.sub.u of the superpositioning gear, and thus small steering wheel moments M.sub.L can be achieved. The resulting very large steering wheel angles .delta..sub.L can be prevented by superimposing suitable motor angles .delta..sub.M, so that the required output angles .delta..sub.L ' can be set with steering wheel angles of the usual size according to the equation:
.delta..sub.L '=.delta..sub.L /i.sub.u +.delta..sub.M
Motor angle .delta..sub.M or its setpoint required for steering support is determined from the steering wheel angle .delta..sub.L Motor angle .delta..sub.M depends on signals representing the movements of the vehicle.
German Patent Application No. 44 46 582 describes a control system containing a higher-level controller and a subordinate controller. The higher-level controller generates signals for influencing actuators. These are actuators for applying braking forces to the wheels. Based on the wheel rpm, control signals are formed in the subordinate controller to control actuators with which a braking force can be applied to the wheels. The signals for influencing the actuators are formed with the help of the higher-level controller so that the controlled variable of the higher-level controller is maintained in a setpoint range within two limit values. The higher-level controller has an influence on the actuators only when the controlled variable of the higher-level controller leaves or is outside the setpoint range.
Systems for controlling driving dynamics of the vehicle are known, for example, from the article "FDR--die Fahrdynamikregelung von Bosch" (Controlling Driving Dynamics by Bosch) which was published in the Automobiltechnische Zeitschrift (ATZ), vol. 96, no. 11 (1994) pages 674 through 689.
The object of the present invention is to improve upon the control of movement parameters representing the motion of the vehicle.